ScrollablePicture.java

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 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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package javademo.swing.scroll.ScrollDemo;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;

import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.Scrollable;
import javax.swing.SwingConstants;

/* ScrollablePicture.java is used by ScrollDemo.java. */

@SuppressWarnings("serial")
public class ScrollablePicture extends JLabel implements Scrollable, MouseMotionListener
{
    
    private int maxUnitIncrement = 1;
    
    private boolean missingPicture = false;
    
    public ScrollablePicture(ImageIcon i, int m)
    {
        super(i);
        if (i == null)
        {
            missingPicture = true;
            setText("No picture found.");
            setHorizontalAlignment(CENTER);
            setOpaque(true);
            setBackground(Color.white);
        }
        maxUnitIncrement = m;
        
        // Let the user scroll by dragging to outside the window.
        setAutoscrolls(true); // enable synthetic drag events
        addMouseMotionListener(this); // handle mouse drags
    }
    
    // Methods required by the MouseMotionListener interface:
    public void mouseMoved(MouseEvent e)
    {
    }
    
    public void mouseDragged(MouseEvent e)
    {
        // The user is dragging us, so scroll!
        Rectangle r = new Rectangle(e.getX(), e.getY(), 1, 1);
        scrollRectToVisible(r);
    }
    
    public Dimension getPreferredSize()
    {
        if (missingPicture)
        {
            return new Dimension(320, 480);
        }
        else
        {
            return super.getPreferredSize();
        }
    }
    
    public Dimension getPreferredScrollableViewportSize()
    {
        return getPreferredSize();
    }
    
    public int getScrollableUnitIncrement(Rectangle visibleRect, int orientation, int direction)
    {
        // Get the current position.
        int currentPosition = 0;
        if (orientation == SwingConstants.HORIZONTAL)
        {
            currentPosition = visibleRect.x;
        }
        else
        {
            currentPosition = visibleRect.y;
        }
        
        // Return the number of pixels between currentPosition
        // and the nearest tick mark in the indicated direction.
        if (direction < 0)
        {
            int newPosition = currentPosition - (currentPosition / maxUnitIncrement) * maxUnitIncrement;
            return (newPosition == 0) ? maxUnitIncrement : newPosition;
        }
        else
        {
            return ((currentPosition / maxUnitIncrement) + 1) * maxUnitIncrement - currentPosition;
        }
    }
    
    public int getScrollableBlockIncrement(Rectangle visibleRect, int orientation, int direction)
    {
        if (orientation == SwingConstants.HORIZONTAL)
        {
            return visibleRect.width - maxUnitIncrement;
        }
        else
        {
            return visibleRect.height - maxUnitIncrement;
        }
    }
    
    public boolean getScrollableTracksViewportWidth()
    {
        return false;
    }
    
    public boolean getScrollableTracksViewportHeight()
    {
        return false;
    }
    
    public void setMaxUnitIncrement(int pixels)
    {
        maxUnitIncrement = pixels;
    }
}